The present invention relates to a method for preparing organoclays from clays including clays purified in the conventional manner and also clays purified as described in a U.S. Patent Application entitled xe2x80x9cPseudophasic Extraction Method for the Separation of Ultra-Fine Mineralsxe2x80x9d having U.S. Ser. No. 09/532,728. More particularly, the invention relates to methods for the surface modification of clays having at least a monomolecular coating of a water-soluble polymer to produce organoclays with improved efficiency and dispersability in aqueous and nonpolar solvents
Organoclays with a wide range of surface wetting characteristics have been described in the patent literature. Surface treatment can be used to render hydrophilic clay surfaces compatible with solvents of decreasing polarity such as alcohols, ethers, aromatic and aliphatic hydrocarbons, and the like. Conventional hydrophilic organoclays have been prepared, wherein a smectite-type clay is surface modified by surface exchange with a water-soluble alkoxylated quaternary ammonium surfactant. The resulting materials are dispersable in water-based systems and can be used for rheology control in products such as latex paints. Other methods for preparing organoclays displaying surface properties ranging from hydrophilic to hydrophobic have been produced by surface modification of the clay through polymer adsorption rather than onium ion exchange. Clay/polymer intercalates have been produced through direct intercalation of the clay with either intercalates have been produced through direct intercalation of the clay with either polymer melts or by contacting a clay slurry with a polymer solution followed by drying. These materials are not readily dispersible in aqueous-based systems but can be used in forming composites with thermoplastic or thermosetting resins.
Traditionally, hydrophobic organoclays have been prepared from a smectite-type clay by surface exchange with high-molecular-weigh quarternary amines, such as demethyl dihydrogenated tallow ammonium chloride, dimethyl benzyl hydrogenated tallow ammonium chloride, and methyl benzyl dihydrogenated tallow ammonium chloride. Another variation described in the literature for making organoclays involves preparation of a hydrophobic organoclay by onium ion exchange followed by intercalation of a hydrophilic or hydrophobic polymer melt. However, this method of producing organoclays does not directly bind the organic polymers to the clay surface. Consequently, these organoclays cannot be dispersed in a solvent system without loss of the polymer from the clay surface which leads to uncontrolled changes in the surface wetting properties of the organoclay. Additionally, these types of organoclay intercalates do not completely exfoliate in the absence of specific chemical polymerization reactions. This method of producing organoclays is further limited to organoclays that have been surface treated with onium ions having carbon chain lengths equal to or greater than 12. The present invention overcomes these, and other problems associated with the production of organoclays.
It is therefore an object of the present invention to provide a novel method for making an organoclay product with enhanced compatibility with aqueous, hydrophilic and hydrophobic systems.
It is another object of the present invention to provide an improved method for making an organoclay product that is fully dispersible in aqueous, hydrophilic and hydrophobic solvents.
It is yet another object of the present invention to provide a novel method for making an organoclay product that is produced with shorter chain onium ions than have been previously produced.
It is another object of the invention to provide an improved method for more precisely controlling the hydrophilic/hydrophobic balance of the clay surface.
It is yet another object of the present invention to provide a novel method for making an organoclay product that is highly dispersible in a solvent system.
It is still another object of the present invention to provide an improved method for making an organoclay having structural and chemical properties which are superior to conventional organoclays for use in the preparation of nanocomposites.
It is another object of the present invention to provide a novel method for making organoclays that can be dispersed in a solvent system without a loss of polymer from the clay surface.
Other objects and advantages of the invention will become apparent by review of the detailed description of preferred embodiments.
The present invention discloses a method for preparing organoclays from clay for use in water treatment applications, as Theological control agents, and in the preparation of nanocomposites. Typically, the clay is dispersed in water, and at least a substantially monomolecular layer of a low-molecular-weight, water-soluble polymer is applied to the basal surfaces of the clay. The clay may include without limitation, kaolin clays, smectite clays, and subgroups thereof including hectorite, montmorillonite, beidelite, stevensite, and saponite clays. A surfactant or surface-modifying polymer is also applied to the clay to modify the hydrophilic/hydrophobic balance (HLB) of the clay surface. Optionally, the resulting organoclay is filtered and dried for subsequent use. Preferably, the organoclay is dried to a moisture content less than about twelve percent by weight. Organoclays designed for use in the preparation of nanocomposites are more preferably dried to a moisture content of less than two percent by weight, and most preferably dried to a moisture content less than 0.5-1 weight percent. Sodium exchange of clays containing multivalent cations in exchange sites, such as, for example, calcium and magnesium, can be accomplished by utilizing an inorganic salt, which also functions to drive exchange reactions with low-molecular-weight onium ions. The disclosed method can further utilize a drying agent which is added to the organoclay prior to drying thereof.
The above described objects and embodiments are set forth in the following description and illustrated in the drawings described hereinbelow.